The intervertebral disc, comprised of an aggrecan-rich nucleus pulposus, surrounded by a ligamentous annulus fibrosus, is a unique structure that permits movement and extension of the human spine. Although it is widely accepted that aging promotes degenerative changes in the disc, the underlying mechanisms of this process are largely unknown. This begs the question: Does responsiveness of nucleus pulposus cells to their microenvironmental conditions change with age? This proposal focuses on the responsiveness to the CCN family of proteins for two reasons: These proteins are known to modulate of growth factor activity and matrix synthesis. Preliminary data shows that CTGF/CCN2 and CCN3 expression changes in the aging and degenerative disc. Both of these observations lend credence to the notion that these proteins are required for maintenance of disc cell function. To address this concept, the following two Specific Aims will be performed. The goal of the first Specific Aim is to test the hypothesis that CTGF and CCN3 regulate survival and extracellular matrix production by nucleus pulposus cells and that responsiveness of cells to these proteins is age-dependent. To test this hypothesis, nucleus pulposus cells isolated from young and aged rats will be treated with rCTGF and rCCN3 and cell survival, sensitivity to apoptogens, and matrix production will be assessed. I will confirm these results using CTGF and CCN3 silenced cells and CTGF null embryos. The objective of Specific Aim 2 is to test the hypothesis that TGFss and hypoxia regulate CTGF and CCN3 expression in nucleus pulposus cells and that regulation is age-dependent. To test this hypothesis, CTGF and CCN3 expression will be measured in nucleus pulposus cells from young and aged rats following treatment with TGFss and in hypoxia. I will measure promoter activity of CTGF and CCN3 in the presence of TGFss and its downstream effectors. I will also determine if the HIF family of transcription factors (HIF-1a and HIF-2a) mediates the regulation of CTGF and CCN3 in hypoxia. Finally, human disc samples of varying grades and age will be analyzed for CTGF, CCN3, and TGFss expression. The information provided by the proposed study will provide insight into the role of CTGF and CCN3 in the aging nucleus pulposus.